Thermochemistry of Fluorinated Dimethyl and Ethyl Methyl Ethers and Corresponding Radical Species

Abstract

Standard enthalpies of formation (Δf H° 298), standard entropies (S°(T)), and heat capacities (C p (T)) are calculated for dimethyl and ethyl methyl fluorinated ethers, both the parent and related radical species. The parent and radical species are utilized to determine carbon–hydrogen, carbon–fluorine, carbon–carbon, and carbon–oxygen bond dissociation energies (C–H, C–F, C–C, and C–O BDEs). The Δf H° 298 and BDEs are calculated using a variety of error-canceling isogyric and/or isodesmic reactions at the MN15/cc-pVTZ, CBS-QB3, and CBS-APNO levels of theory. Δf H° 298 calculations from the MN15 functional for these ether species are shown to have consistency with the CBS-QB3 and CBS-APNO composite methods with our recommended ideal gas phase Δf H° 298 values from the average of these two composite methods. C–F BDE values are shown to range overall between 111 and 128 kcal mol–1, the C–H BDEs are in the 93–106 kcal mol–1 range, the C–O BDEs are in the 83–107 kcal mol–1 range, and the C–C BDEs are in the 88–101 kcal mol–1 range. It is observed that as the number of fluorine atom substitutions increases, the C–H BDEs also increase. The number of fluorine atom substitutions on the carbon atom where the C–F bond is being broken has a larger influence than that of the total number of fluorine atom substitutions in the species. Optimized geometry parameters, moments of inertia, vibrational frequencies, and single bond internal rotor potentials are calculated at the MN15/cc-pVTZ level for contributions to entropy and heat capacities. Calculated thermochemical properties for CF-C-O-C, C-CF-O-C, and C-C-O-CF (i.e., 1-fluoroethyl methyl ether, 2-fluoroethyl methyl ether, and ethyl fluoromethyl ether) are utilized to develop fluorinated group additivity values (C/C/F/H2, C/C/F/H/O, and C/F/H2/O) for use in the group additivity (GA) method (as well as several carbon–hydrogen bond increment groups corresponding to radical formation). This work is of value in the development of detailed chemical kinetic mechanisms for use in atmospheric chemistry.

Extensive High-Accuracy Thermochemistry and Group Additivity Values for Halocarbon Combustion Modeling

“…With advances in ab initio quantum chemistry methods and codes, recent studies use high-level ab initio composite schemes and/or isodesmic reactions to calculate thermochemical properties such as within or close to chemical accuracy (1 kcal/mol). Included in many of these studies are group additivity values (GAVs), in particular the works of Bozzelli and co-workers. − Since conventional group additivity does not work well for chlorocarbons, Chen and Bozzelli introduced a modified scheme which uses non-next-nearest neighbor interaction terms (NNNI) to account for the destabilizing interaction between electronegative chlorine atoms on adjacent carbons . This modified NNNI–GAV scheme was later extended to fluorine–fluorine interactions in HFCs and chlorine–oxygen interactions in chlorinated hydroperoxides …”

Extensive High-Accuracy Thermochemistry and Group Additivity Values for Halocarbon Combustion Modeling

“…Included in many of these studies are group additivity values (GAVs), in particular the works of Bozzelli and coworkers. [12][13][14][15][16][17][18] Since conventional group additivity does not work well for chlorocarbons, Chen and Bozzelli introduced a modified scheme which uses nonnext-nearest neighbor interaction terms (NNNI) to account for the destabilizing interaction between electronegative chlorine atoms on adjacent carbons. 19 This modified NNNI-GAV scheme was later extended to fluorine-fluorine interactions in HFCs 12 and chlorine-oxygen interactions in chlorinated hydroperoxides.…”

“…from the Active Thermochemical Tables (ATcT) 47 and various literature sources. [13][14][15][16][17][18][22][23][24][27][28][29][30] With a mean absolute error (0.83 kcal/mol) within chemical accuracy (≤ 1 kcal/mol), G4 is a suitable, relatively low cost composite quantum chemistry method for high-fidelity and high-throughput calculations of HHCs. However, for heavily halogenated systems, G4 and other composite methods do not compute enthalpies within chemical accuracy.…”

Extensive High-Accuracy Thermochemistry and Group Additivity Values for Halocarbon Combustion Modeling

“…Included in many of these studies are group additivity values (GAVs), in particular the works of Bozzelli and coworkers. [12][13][14][15][16][17][18] Since conventional group additivity does not work well for chlorocarbons, Chen and Bozzelli introduced a modified scheme which uses nonnext-nearest neighbor interaction terms (NNNI) to account for the destabilizing interaction between electronegative chlorine atoms on adjacent carbons. 19 This modified NNNI-GAV scheme was later extended to fluorine-fluorine interactions in HFCs 12 and chlorine-oxygen interactions in chlorinated hydroperoxides.…”

“…from the Active Thermochemical Tables (ATcT) 47 and various literature sources. [13][14][15][16][17][18][22][23][24][27][28][29][30] With a mean absolute error (0.83 kcal/mol) within chemical accuracy (≤ 1 kcal/mol), G4 is a suitable, relatively low cost composite quantum chemistry method for high-fidelity and high-throughput calculations of HHCs. However, for heavily halogenated systems, G4 and other composite methods do not compute enthalpies within chemical accuracy.…”